This invention relates to an imaging element containing a blocked photographically useful compound, such as a developer.
The photographic arts have a longstanding history of attempts to supply customers with convenient and simple ways to take pictures that serve to record their everyday lives. Conventional color photography has attempted to meet this need by supplying light sensitive silver halide containing films suitable for use in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form image.
The well known chromogenic dye-forming films require reducing agents such as p-aminophenols or p-phenylenediamine developers to form dye images. These reducing agents are typically present in developer solutions which are then brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements frequently leads to desensitization of the silver halide emulsion and undesirable fog. Considerable effort has therefore been directed at trying to produce effective blocked developers, which can be introduced in silver halide emulsion elements without deleterious desensitization or fog effects and which un-block under conditions of development so that developer is free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599, to Reeves, discloses the use of Schiff base developer precursors. Schleigh and Faul, in a Research Disclosure (129 (1975) pp. 27-30), described the quaternary blocking of color developer and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND). Subsequently, U.S. Pat. No. 4,157,915, to Hamaoka et al., and U.S. Pat. No. 4,060,418, to Waxman and Mourning, describe the preparation and use of blocked p-phenylenediamines in an image receiving sheet for color diffusion transfer.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, and lack of simple methods of releasing the blocked developer.
Recent developments in blocking and switching chemistry have led to blocked p-phenylenediamines that perform well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development.
The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
The incorporation of these blocked developers in photographic elements is typically carried out using colloidal gelatin dispersions of the blocked developers. These dispersions are prepared using means well known in the art, wherein the developer precursor is dissolved in a high vapor pressure organic solvent (for example, ethyl acetate), along with, in some cases, a low vapor pressure organic solvent (such as dibutylphthalate), and then emulsified with an aqueous surfactant and gelatin solution. After emulsification, usually done with a colloid mill, the high vapor pressure organic solvent is removed by evaporation or by washing, as is well known in the art.
Thus there is a continuing need for an image-forming element and process that provides consumers with simple and convenient ways to take pictures. In particular, there is a continuing need for imaging elements, particularly photographic and photothermographic imaging elements, that contain a developer in a form that is stable until development yet can rapidly and easily develop the imaging element once processing has been initiated by heating the element and/or by applying a processing solution, such as a solution of a base or acid or pure water, to the element without the necessity of the presence of a dinucleophile. The existence of such a developer chemistry will allow for very rapidly processed films that can be processed simply and efficiently in low cost photoprocessing kiosks.
Similarly, there is a need for incorporating other photographically useful compounds into a photographic element such that they remain stable until processing and are then rapidly released. Such photographically useful compounds include, couplers, dyes and dye precursors, electron transfer agents, etc., as discussed more fully below.
This invention relates to a compound having a heteroaromatic moiety that enables release of a photographically useful group on thermal activation. In a preferred embodiment the photographically useful group is a developer.
In one embodiment, thermal activation preferably occurs at temperatures between about 100 and 160xc2x0 C. In another embodiment, thermal activation preferably occurs at temperatures between about 20 and 100xc2x0 C. in the presence of added acid, base or water.
The invention further relates to a light sensitive photographic element comprising a support and a compound having a heteroaromatic moiety that enables release of a photographically useful group on thermal activation.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a heteroaromatic moiety that enables release of a photographically useful group on thermal activation to form a developed image, scanning said developed image to form a first electronic image representation from said developed image, digitizing said first electronic record to form a digital image, modifying said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a compound having a heteroaromatic moiety that enables releases of a photographically useful group on thermal activation.
The invention further relates to a method of image formation having the steps of imagewise exposing a light sensitive photographic element comprising a support and a compound having a heteroaromatic moiety that enables release of a photographically useful group on thermal activation in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
A more preferred embodiment of the invention comprises an imaging element comprising an imaging layer having associated therewith a compound of Structure I: 
wherein
PUG is a photographically useful group;
LINK 1 and LINK 2 are linking groups;
TIME is a timing group;
T represents t independently selected substituted or unsubstituted alkyl (preferably containing 1 to 6 carbon atoms) or aryl groups (preferably phenyl or naphthyl), t is 0, 1, or 2 and if t is 2, the T groups can form a ring;
HET is a heterocyclic group which optionally can form a ring with a T group;
R12 is hydrogen, substituted or unsubstituted alkyl or substituted or unsubstituted aryl, or R12 can form a ring with a T group or with HET;
l is 0 or 1;
m is 0, 1, or 2; and
n is 0 or 1.
In a preferred embodiment of the invention, LINK 1 and LINK 2 are of structure II: 
wherein
X represents carbon or sulfur;
Y represents oxygen, sulfur or Nxe2x80x94R1, where R1 is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1;
with the proviso that when X is carbon, both p and r are 1, when X is sulfur, Y is oxygen, p is 2 and r is 0;
# denotes the bond to PUG (for LINK 1) or TIME (for LINK 2):
$ denotes the bond to TIME (for LINK 1) or T(t) substituted carbon (for LINK 2).